You think you’re so clever. You think you’re gaming the system. You hardly put any information on Facebook anyway–you just use it to lurk and occasionally “poke” people–so how can Facebook be mining data, targeting ads, or making money off you at all?

Think again.

A patent application from earlier this month shows that Facebook appears to be finding ways to infer your interests, even though your profile is bare, by looking at the interests of your friends. The theory is that if all your buddies simply adore Mountain Dew, or whatever, then the laws of peer pressure probably mean that you do, too. Reads one section of the patent application: “Rather than missing out on the opportunity to target ads to this latter group of members”–that is, you information hoarding free riders–“embodiments of the invention use the information for other members to whom a particular member is connected.”

The patent application is dated October 7, 2010, though it was initially filed back in ’09. An eagle-eyed blogger over at CNET just spotted it today. The inventors of the system are listed as Ding Zhou, a Facebook engineer, and Timothy Kendall, its director of monetization. The application’s title is “Leveraging Information in a Social Network for Inferential Targeting of Advertisements.”